The invention relates to a compensation element for joining components made of fusible plastics which is, at least in sections, configured as a conically shaped hollow cylinder, comprising at least one heating element which, when supplied energy, heats at least some regions of the inner surface or the outer surface of the compensation element or of both surfaces, for producing a welded joint with said components.
Such compensation elements, also referred to as heating sleeves or welding sleeves, have been known for a long time. They are mainly provided for producing inseparable joints between plastic pipes or plastic pipes and their fittings.
For example, FR-A-1 416 217 shows how two pipes may be welded by means of a conical sleeve which comprises a heating element. The pipes themselves comprise conicities mating to the conicity of the heating sleeve both on its inner side and on its outer side.
DE-A-24 19 893 discloses a pipe joint with the aid of a double sleeve, the inner sides thereof being configured in the shape of a truncated cone. The pipes to be joined are pushed into said double sleeve from its both ends and are welded together by means of a conical joining element, which is referred to as a welding joint or welding member, however, is not described in detail.
In an approach according to DE-A-34 22 074, a pipe and a sleeve are conically calibrated, similar as in FR-A-1 416 207, wherein the tolerance gap between pipe and sleeve is dimensioned according to the size of a heating sleeve which is to be inserted at a later date.
JP-B-52 066 532 also shows a conical welding sleeve, wherein a continuous slit provides that it can be modified in its radial dimension.
Another conical welding sleeve, which may be formed having perforations or as a mesh, is shown in U.S. Pat. No. 3,061,503.
A compensation element or a sleeve, respectively, of the kind set forth in the introductory is in particular known from WO 02/11973 and serves to join a pipe of a fuel line with a fuel tank. The compensation element contains said heating element both on its outer surface and its inner surface and is introduced into an angular gap between the components to be joined together, whereupon the welding occurs.
DE 10 81 288 discloses a method for joining a pipe and a sleeve by means of interposition of a wedge-shaped welding sheath. A conical outer surface of the sheath is thereby fitted into the conical inner surface of the sleeve, so that after positive sticking together of pipe, sleeve and sheath, the sheath extends some millimeters beyond the sleeve. During the welding process, the sheath is pressed into the conus of the sleeve by means of a gripper.
Such compensation elements have perfectly proven their worth for small pipe diameters. For larger pipe diameters, however, which may be absolutely in the magnitude of 1,000 mm or above, the manufacturing tolerances are so broad that gaps between components occur which complicate, if not prevent a fluid-tight welding, and this despite of the conicity of the sleeve which, also without preceding calibration of the components to be joined, provides for a certain tolerance compensation. The problem gets worse, if, for example, a pipe is irregular.